As is pointed out in the co-owned U.S. Pat. No. 4,399,028, froth flotation apparatus is well-known for the separation of small contaminant particles from liquid suspension stock, and the assignee of that patent is particularly interested in the development and manufacture of froth flotation apparatus for use in the de-inking of waste paper furnishes so that the resulting stock can be reused for the manufacture of paper. For example, the paper making industry presently has great interest in the deinking of used newsprint and also in the de-inking of waste white papers, such as ledger papers, to produce a stock which can be used in the manufacture of tissue.
The above patent discloses froth flotation apparatus comprising a generally cylindrical side wall and internal partitions which cooperate to define a plurality of vertically stacked, annular flotation cells surrounding a common discharge conduit for froth. The stock suspension to be de-inked or otherwise cleaned is supplied to the top cell by an inlet which includes provision for aerating the stock as it is delivered into the cell. The contaminant-containing froth which develops on the top of the liquid in the uppermost cell is skimmed off into the froth discharge conduit, while the stock cleaned in passing through that cell is delivered to the next lower cell, again accompanied by aeration, and the same process is repeated in each of the lower cells successively as stock passes therethrough to the outlet conduit for accepted stock from the lowermost cell.
In that patent, the mechanism for aerating the stock as it is delivered into each cell comprises a hollow cylinder member of porous material, such as sintered bronze, mounted for rotation in the path of the stock suspension being delivered to each cell on an axis extending transversely of the inlet conduit to the cell. Compressed air is supplied to the interior of this cylinder while it is being rotated, and passage of the air through and discharge from the pores in the cylinder produce bubbles which effect the desired aeration of the stock and the creation of froth within the cell.
The above-identified application discloses an improved aerating mechanism for incorporation in froth flotation apparatus--known as a "sparger"--which provides a highly effective aerating action on the stock delivered to froth flotation apparatus while requiring substantially less power consumption than existing apparatus for the same purpose, and which at the same time produces more effective mixing of all constituents of the supply stock, including whatever chemicals may be added thereto, than is accomplished by conventional apparatus.
The primary active component of the sparger of that application is a drum-like rotor which is mounted for rotation on an axis extending transversely of the stock inlet conduit to each cell, and which has an irregular outer surface, e.g. multiple circumferentially spaced ribs or other protuberances, capable of a mixing and/or shearing action. The stock inlet conduit is also provided with an air supply conduit extending into it from upstream of the rotor and having a discharge nozzle which extends the full width of the rotor and is positioned in close relation to the surface of the rotor on the upstream side thereof so that only a running clearance is provided therebetween.
In the operation of that apparatus, the liquid stock suspension is delivered to the cell through the inlet conduit at a flow velocity which may be relatively low, but the rotor is driven at a rate which will cause its outer surface to travel at a relatively high speed past the outlet end of the air nozzle. This surface passes the nozzle outlet at a desired high speed, thereby drawing air from the nozzle into the stock inlet conduit and simultaneously mixing that air with the surrounding stock.